With a contact plate of the known type, it may be the case of a bipolar plate or an end plate for a fuel cell stack, or also of a monopolar plate for an individual fuel cell or fuel cells arranged in a plane. Such contact plates have several functions. On the one hand they serve for ensuring an electrical conductive connection to an adjacent layer with which it is the case of a gas diffusion layer, an electrode, an electrolyte membrane or a further fuel cell, on the other hand for supplying or the leading-away of reactands and/or reaction products, for which a channel structure is provided, and further also for leading-away reaction heat. In particular for mobile applications, a manufacture of contact plates from metal may be desirable since the larger mechanical stability of metal compared to other materials permits a compacter construction of fuel cells and fuel cell stacks.
At the same time a further problem exists due to the fact those metals which are adequately corrosion-resistant in order to withstand the aggressive conditions usually prevailing in the fuel cells and which may considered with regard to their economical aspects, tend to undergo passivation. Thus for example stainless steel forms a passive layer of chromium oxide, by which means does a corrosion resistance result at all. A passive layer however leads to a considerably increased electrical contact resistance, by which means the function of a contact plate of creating an electrical connection which is low in losses, is compromised to beyond an acceptable level.
It is known to circumvent this problem by way of a coating of contact plates. Thus for example the document EP 1 107 340 A2 discloses a contact plate of the known type for fuel cells, with an active area which is envisaged for contact on a diffusion layer and which comprises recesses next to a contact surface so that the recesses form a channel structure, wherein the active area has a coating of a conductive, corrosion-resistant material. With this, according to the state of the art not only is the contact surface provided for contact on an adjacent layer, but also the whole active area including recesses is coated. Such an embodiment is suggested by way of deposition techniques for the coating which have been used until now, but however entails the significant disadvantage that extremely large quantities of coating material are required. Since very costly materials are commonly used as a coating material, for example gold or platinum, excessively high manufacturing costs therefore arise. Furthermore the complete-surfaced, non-selective coating of the active area involves the danger that the flow properties of the contact plates are changed to a significant extent due to the accumulation of the coating material in the bottom region of the recesses/channel structures.